Historic, Archive Document Do not assume content reflects current scientific knowledge, policies, or practices. OBSERVATIONS on the NODULA7ION or LEGUMINOUS Pi At ITS Of THE SOUTHWEST Regional Bulletin No : 107 Plant Study Series No. 14. Novsniber 12, I9I4.3 r v by JT. P. Martin in cooperation with . 6- L, N» Goodding L, p. Hamilton y Lyina n Ben s on an d Joel E. Fj.etche:r I BR A R 1 , rial \ RlAl StCOfiD JUN13 ,349 ivy UNITED states department of agriculture Soil Conservation Service, Region 6 Albuquerque, New Mexico OBSERVATIONS ON THE NODULATION OF LEGUMINOUS PLANTS IN THE SOUTHWEST By W. P. Martin U ^1 with the cooperation of: L, N« Goodding, L. P. Hamilton, Lyman Benson, and Joel E, Fletcher Why the Investigations and Observations Were Hade Plants of the family Leguminosae are found widely distributed in the Southwest and often constitute an appreciable part of the flora of a given site, whether it be desert or high mountain meadow. An important characteristic of these plants is that they often contain root nodules in which are growing in symbi- otic relationship nitrogen-fixing bacteria of the genus Rhizobium. Leguminous plants therefore are considered to be "soil builders" because they can, in association with the root-nodule bacteria, take nitrogen from the atmosphere and eventually add it to the soil where it can be used by associated non- leguminous plants. Leguminous plants have been considered to be of particular importance by the soil conservationist since they may flourish in badly eroded soils where nitro- gen is a limiting factor for the growth of other plants. It has often not been realized, however, that nodulation and subsequent nitrogen-fixation cannot be taken for granted in the development of a leguminous plant. The proper species of bacteria must be present in the soil to produce root nodules or must be sup- plied artificially by way of inoculation. The bacteria which produce nodules on different leguminous plants are not universally distributed in the soil. In addition to this, it is now well known that many of the bacteria which do produce nodules are not active nitrogen fixers and may in certain instances even be parasitic on the plant. There are some leguminous plants which do not produce nodules under any circumstances, Cursory examination of many legumi- nous-plants in the field, extending over several years, did not show root nodules to be present and abundant in many instances. Most nodules observed did not appear to be healthy and were thinly scattered over the root system. It was consequently thought desirable to study the nodulation of leguminous plants native to the Southwest and of certain introduced species which are being tested out in Soil Conservation Service nurseries for possible use in this area. A preliminary report on some of the results of these investigations follows: 1/ Soil Conservation Service and University of Arizona, cooperating. 2/ Now forest ecologist, Southwestern Forest and Range Experiment Station, Forest Service, U. 3. Department of Agriculture. Procedure The method of procedure was threefold: (a) Field trips were taken into different parts of Arizona and New Mexico for the purpose of collecting soil samples from the different environments where leguminous plants were found. The collected soil samples were to be used as inoculants for seed to be grown in the greenhouse. At the time of soil sample collection, leguminous plants were identified or collected for later identifi- cation and insofar as possible the root systems were examined for the charac- teristic root nodules. This method of examination was not entirelv successful since the soils were often dry and difficult to break away from the root sys- tems without destroying them. Furthermore , the plants were found in different stages of maturity. (b) Consequently, when available, seed of the various leguminous plants were obtained primarily from the Soil Conservation Service but also from the field and grown in a greenhouse under more or less idealized conditions. Greenhouse sand was mixed with soil which had been collected in the field from the roots of the same plant growing under natural conditions. When the plants had reached satisfactory size, generally the seedling stage or just beyond, the entire root system was examined after carefully washing away the sand and soil particles. In most instances several soils vrere used which represented the range of er vironmcntal conditions observed in the field to support the growth of the particular leguminous plant being tested. (c) The third method of procedure was to grow plants at the Soil Conservation Service Nursery in Tucson from seed and inoculate them with pure cultures of the bacteria in the usual manner. The cultures used, however, were of a "shot- gun" variety made up of species of several of the cross-inoculation groups, since it was not known in most instances to which cross-inoculation group the different species belonged. During growth the plants on several occasions were dug up from the sandy soil of the nursery, the roots washed out against a screen, using a gentle stream of water, and examined for the presence of nodules In all instances adjective descriptions of the judgment of the observer on the kind of nodulation were noted, i.e., "good to excellent," "poor to fair." This was based on number of nodules, whether or not they were in healthy condition, and whether or not they were scattered thinly through the smaller rootlets or clustered around the major tap root or principal arteries. This work was initiated by and under the immediate direction of Louis P. Hamilton, Soil Con- servation Service Nursery manager at Tucson. Results The following three lists have been • prepared more or less as check lists for the results obtained in these experiments. It is realized that the investiga- tion has by no means been exhaustive and that many changes will subsequently have to be made as more observations are obtained or greater experience is had with the different species under natural growth conditions. Some of the plants which did not here contain nodules may, under a proper comDination of environ- mental conditions, support a large number of them. Some of the plants which - 2 - showed poor nodulation may, under other circumstances , show excellent nodula- tion. However, these results are considered of importance in that they will tend to emphasize the fact that the nodulation of native legumes is ' not some- thing which can be taken for granted; that the native legume is not always a soil builder; and that for their best use for e^o-sion control, these plants may be enhanced by the proper nodulation. To determine how to obtain proper nodulation in all instances will require much additional study and investiga- tion. List No. 1: Species of leguminous plants observed to have root nodules under one or more of the following conditions: 1 - Under natural conditions in the field. 2 - At the SCS Nursery, either with or without inoculation of the seed with commercial inoculant (a mixture of cultures from several "cross inoculation" groups) or 3 - In greenhouse pots after inoculation of the seed with soil collected from roots of the "wild" legume. Species l/ +Ae s chynomene americana l/ -fAmorpha fruticosa * Astragalus sp. •(Astragalus austrinus l/ -fAstragulus lonchocarpus l/ ^Astragalus nuttallianus -fCrotalaria lupulina l/ *Coronilla varia +Dalea frutescens + Da lea lagopus +Dalea lumholtzi 4Dalea ordeae •f Da lea parryi ■fDalea pogonanthera *Dalea sanctae crucis SCS Accession Number of Seed ~~~~~ A 2926 A 2101, A 1850, A 2102, A 2103 A 9655 A 968U A 9653 ii. 1907 A 8I63 A 2812 ■A 8250 A 82 7U A 2323 A 8917 -^Native to Southwest ♦Good to excellent nodulation, both in field and greenhouse. l/Species also reported by others to bear nodules. See Appendix I for explanation. Unstarred species, poor to fair nodulation - 3 - List No. 1, continued Species l/ 4D'esmanthus virgatus 4Desmodium sp. 4Desmodium batocaulis l/ 4Hedysarum coronarium l/ *Lathyrus latifolius l/ Leucaena glauca 4Lotus alamos anus l/ *4 Lotus cornioulatus 4 Lotus corniculatus var. ciliatus 4/Lotus greenei Lotus grandif lorus 4 Lotus humi stratus •rLupinus sp. 4Lupinus sparsiflorus l/ *MedicagQ orbicularis 1/ *Mili lotus alba Onobrychis chorissanica ♦Onobrychis vulgaris Phaseolus sp. 4Rynchosia texana 4Thermopsis montana 4Trifolium brandegei l/ *Tri folium dub i urn 1/ *,J-'ri folium fragiferum l/ *Tri folium lappaceuni *Tri folium resupinatum 1/ *THfoIi urn subterraheum l/ Trigonella foenum graecum *Vicia amoena l/ *Vicia cracca *4"'7icia exigua l/ *4Vicia noeana *Vicia villosa SCS Accession Uumber of Seed A 9G33 ■ ' • A' 8866, A 9137, A 11358 A 9312 A 9998 A ll6l& ; A 9^72 A 89/'+5 A U22 A 9371 A 9988 A 11171 A II697 A 157^ and 1733 A 2123 A 965O A 11345 A 8258 A 9U21 A II698 A 11258 A 1162 A 11688 A II634 A 10601 A 9626 A 9623 A 3150 A 1727 A 5518 - k - List No. 2 Species of leguminous plants not containing root nodules. Plants examined in the field after inoculation of seed with commercial inoculant and in greenhouse after inoculation of the seed with soil collected in the field from roots of the same species growing under natural conditions. •pecies SCS Accession Lumber of Seed 4Acacia greggi 2/ 2/ +Acacia suf f rutescens Astragalus alopecios Astragalus ammodendron-conf irmans Astragulus campyloninchus Astragulus chirvensis Astragalus cicer Astr a°;alus filicaulis Astragalus rubyi -f Benthamantha edwardsi •(■Cassia covesi ■fCassia leptocarpa ■f Cere Ldi um torreyanum Coronilla glauca Coronilla juncea Dalea sp. ■f-Dalea albiflora •f Da lea amoena Dalea batocaulis ea mollis ■f Dalea wrighbi 2/ Desmodium purpureum Desmodium supina -/Eysenhardtia orthocarpa -fC-alactia wrighti •fHedysarum pabulare A 1 0?1 1 A h A 16?8 A 1680 l^S .a 1683 JX 963O A *k 1^27 Jik 1T2S7 1 \ 8713 ax 9661 A 9559 XX 3270' ft XX 287 A 288 A 8 165 .4 -L JL Q^IS A 8871 A 11358 A 9502 A 95U3 A 9923 A IIU96 xX 9520 XX 9175 Ik 91+03 2/ Species which have been reported by others to bear nodules appendix 1 for explanation. 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